The inventive subject matter generally relates to power control for a light source for a handheld medical instrument for intracorporeal use. The inventive subject matter particularly relates to solid state lighting sources, such as LEDs, used in an endoscope.
Although not limited to the use in an endoscope, the inventive subject matter will be illustrated by reference to endoscopic light systems, particularly those using electronic image sensors and LED light sources disposed on or in an endoscope.
In order to eliminate the heavy, bulky and awkward fiberoptic “light pipe” from a conventional light source (i.e., 300W Xenon), high-power, white LEDs are currently used as an endoscope light source. The LEDs are contained in the body of an digital endoscope. Such LEDs, while more efficient than a conventional light source, produce some significant heat when operating at a high light output. Accordingly, there is a need to control the temperature of the body of the endoscope to a maximum of about 40° C. to meet with operator comfort or safety requirements, and preferably to keep the instrument temperature even lower than that for operator comfort and confidence.
Current designs vary the output of the LEDs as part of the electronic exposure system and strive to keep the temperature below the prescribed limit by simply setting a maximum current limit. If the imaging system senses a situation with insufficient light, it increases LED output up to the maximum, if needed, and keeps it there if the scene still seems to be insufficiently lit. A drawback to the approach of a set maximum power to the LEDs to control the temperature is that the potential of using a higher LED output capability for short periods of time is compromised.
Another problem with current LED systems is their failure to intelligently adapt to state of activity. For example, it is not uncommon for an electronic endoscope to be placed on a table or cart and left for some period of time, with the end pointing toward objects much farther away than the designed operating distance of the endoscope, with lighting conditions which the endoscope will determine as insufficient. These conditions can set the LED drive to its maximum output, and the handle will heat up to the set maximum temperature. A user coming back to pick up the endoscope will sense a rather hot object.
Accordingly, there is a need for improved illumination systems with automated temperature control and intelligent adaptation to their state of activity.